Stamped bipolar plate for PEM fuel cell stack

ABSTRACT

A bipolar plate assembly for a PEM fuel cell having a serpentine flow field formed on one side and interdigitated flow field formed on the opposite side such that a single plate member are usable for as an anode current collector and a cathode current collector of adjacent fuel cells. The bipolar plate assembly further includes a staggered seal arrangement to direct gaseous reactant flow through the fuel cell such that the seal thickness maximized while the repeat distance between adjacent fuel cells is minimized.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application No.09/791,528 filed on Feb. 23, 2001, now U.S. Pat. No. 6,503,653. Thedisclosure of the above application is incorporated herein by reference.

TECHNICAL FIELD

This invention relates to PEM fuel cells and more particularly tobipolar plates for separating adjacent fuel cells in a fuel cell stack.

BACKGROUND OF THE INVENTION

Fuel cells have been proposed as a power source for many applications.One such fuel cell is the proton exchange membrane or PEM fuel cell. PEMfuel cells are well known in the art and include in each cell thereof aso-called “membrane-electrode-assembly” or MEA comprising a thin,proton-conductive, polymeric, membrane-electrolyte having an anodeelectrode film formed on one face thereof, and a cathode electrode filmformed on the opposite face thereof. Such membrane-electrolytes are wellknown in the art and are described in such as U.S. Pat. Nos. 5,272,017and 3,134,697, as well as in the Journal of Power Sources, Volume 29(1990) pages 367-387, inter alia.

In general, such membrane-electrolytes are made from ion-exchangeresins, and typically comprise a perfluoronated sulfonic acid polymersuch as NAFION3 available from the E. I. DuPont de Nemeours & Co. Theanode and cathode films, on the other hand, typically comprise (1)finely divided carbon particles, very finely divided catalytic particlessupported on the internal and external surfaces of the carbon particles,and proton conductive material such as NAFION3 intermingled with thecatalytic and carbon particles, or (2) catalytic particles, sans carbon,dispersed throughout a polytetrafluoroethylene (PTFE) binder. One suchMEA and fuel cell is described in U.S. Pat. No. 5,272,017 issued Dec.21, 1993, and assigned to the assignee of the present invention.

The MEA is sandwiched between sheets of porous, gas-permeable,conductive material which press against the anode and cathode faces ofthe MEA and serve as (1) the primary current collectors for the anodeand cathode, and (2) mechanical support for the MEA. Suitable suchprimary current collector sheets comprise carbon or graphite paper orcloth, fine mesh noble metal screen, and the like, as is well known inthe art. This assembly is referred to as the MEA/primary currentcollector assembly herein.

The MEA/primary current collector assembly is pressed between a pair ofnon-porous, electrically conductive plates or metal sheets which serveas secondary current collectors for collecting the current from theprimary current collectors and conducting current between adjacent cellsinternally of the stack (i.e., in the case of bipolar plates) and at theends of a cell externally of the stack (i.e., in the case of monopolarplates). The secondary current collecting plate contains a flow fieldthat distributes the gaseous reactants (e.g., H₂ and O₂/air) over thesurfaces of the anode and cathode. These flow fields generally include aplurality of lands which engage the primary current collector and definetherebetween a plurality of flow channels through which the gaseousreactants flow between a supply header at one end of the channel and anexhaust header at the other end of the channel.

Conventionally, these metal plates have a single functional flow fielddefining a particular geometry of the flow channel. One generally knownflow field defines serpentine flow channels which connect the supply andexhaust header after making a number of hairpin turns and switch backs.Serpentine flow channels thus define a contiguous, albeit tortuous flowpath. Another generally known flow field defines interdigitated flowchannels in which a plurality of flow channels extending from the supplyheader towards the exhaust header but terminating at deadends areinterdigitated between a plurality of flow channels extending from theexhaust header towards the supply header but terminating at deadends. Incontrast to serpentine flow channels, these interdigitated flow channelsdefine a noncontiguous path such that flow between the supply andexhaust header is achieved when the gaseous reactants traverses a landbetween adjacent flow channels through the porous primary currentcollector.

Conventionally, a bipolar plate is formed by assembling a pair of metalsheets such that a functional flow field is formed on each side of thebipolar plate assembly. Often times a spacer is interdisposed betweenthe metal sheets to define an interior volume to permit coolant flowthrough the bipolar plate assembly. One such bipolar plate assembly isdescribed in U.S. Pat. No. 5,776, 624 issued Jul. 7, 1998, and assignedto the assignee of the present invention.

SUMMARY OF THE INVENTION

The present invention is directed to a stamped bipolar plate having asingle metal sheet which defines functional flow fields on oppositesides thereof. The metal sheet incorporates a porting scheme which whencombined with a staggered seal configuration directs the flow of gaseousfuel to one side of the plate and the flow of gaseous oxidant to theother side of the plate.

The present invention includes a bipolar plate formed from a singlemetal sheet having a serpentine flow field on one side of the plate andan interdigitated flow field on the opposite side of the plate. Theformed metal sheet maintains a generally uniform wall thickness toproduce an uncooled bipolar plate from a single sheet. A pair of bipolarplates may be layered together with a spacer there between to produce abipolar plate with internal cooling channels.

The flow field geometry of the present invention is such that a pressuredifferential occurs across most areas where the plate touches the porousprimary current collectors resulting in a higher performance thanconventional bipolar plate assemblies.

The present invention further incorporates a staggered sealconfiguration which in conjunction with a specific port geometrycommunicates gaseous reactants to each cell without requiring additionalparts or components to carry the seal load.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood when considered in the light ofthe following detailed description of a specific embodiment thereofwhich is given hereafter in conjunction with the several figures inwhich:

FIG. 1 is a schematic isometric exploded illustration of a PEM fuelstack;

FIG. 2 is an isometric exploded view of an MEA and bipolar plate in afuel cell stack;

FIG. 3 is an isometric view of a portion of the top surface of thebipolar plate illustrated in FIG. 2 having a serpentine flow fieldformed thereon;

FIG. 4 is a plan view of the top of the bipolar plate illustrated inFIG. 2;

FIG. 5 is an isometric view of a portion of the bottom surface of thebipolar plate illustrated in FIG. 2 having an interdigitated flow fieldformed thereon;

FIG. 6 is a plan view of the bottom of the bipolar plate illustrated inFIG. 2;

FIG. 7 is a cross section of a bipolar plate and porous primary currentcollectors in a fuel cell stack illustrating the direction of reactantgas flow;

FIG. 8 is an isometric exploded view of a pair of fuel cells includingan uncooled cell and a cooled cell in a fuel stack;

FIG. 9 is a plan view of the fuel cell stack illustrated in FIG. 8;

FIG. 10 is a cross section taken along line X—X of FIG. 9 showing theanode porting;

FIG. 11 is a cross section taken along line XI—XI of FIG. 9 showing theanode porting;

FIG. 12 is a cross section taken along line XII—XII of FIG. 9 showingthe cathode porting;

FIG. 13 is a cross section taken along line XIII—XIII of FIG. 9 showingthe cathode porting; and

FIG. 14 is a cross section taken along line XIV—XIV showing the coolantporting.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 schematically depicts a partial PEM fuel cell stack having a pairof membrane-electrode-assemblies (MEAs) 8 and 10 separated from eachother by a non-porous, electrically-conductive bipolar plate 12. Each ofthe MEAs 8, 10 have a cathode face 8 c, 10 c and an anode face 8 a, 10a. The MEAs 8 and 10, and bipolar plate 12, are stacked together betweennon-porous, electrically-conductive, liquid-cooled bipolar plates 14 and16. The bipolar plates 12, 14 and 16 each include flow fields 18, 20 and22 having a plurality of flow channels formed in the faces of the platesfor distributing fuel and oxidant gases (i.e., H₂ & O₂) to the reactivefaces of the MEAs 8 and 10. Nonconductive gaskets or seals 26, 28, 30,and 32 provide a seal and electrical insulation between the severalplates of the fuel cell stack. Porous, gas permeable, electricallyconductive sheets 34, 36, 38 and 40 press up against the electrode facesof the MEAs 8 and 10 and serve as primary current collectors for theelectrodes. Primary current collectors 34, 36, 38 and 40 also providemechanical supports for the MEAs 8 and 10, especially at locations wherethe MEAs are otherwise unsupported in the flow field. Suitable primarycurrent collectors include carbon/graphite paper/cloth, fine mesh noblemetal screens, open cell noble metal foams, and the like which conductcurrent from the electrodes while allowing gas to pass therethrough.

Bipolar plates 14 and 16 press up against the primary current collector34 on the cathode face 8 c of MEA 8 and primary current collector 40 onthe anode face 10 a of MEA 10, while the bipolar plate 12 presses upagainst the primary current collector 36 on the anode face 8 a of MEA 8and against the primary current collector 38 on the cathode face 10 c ofMEA 10. An oxidant gas such as oxygen or air is supplied to the cathodeside of the fuel cell stack from a storage tank 46 via appropriatesupply plumbing 42. Similarly, a fuel such as hydrogen is supplied tothe anode side of the fuel cell from a storage tank 48 via appropriatesupply plumbing 44. In a preferred embodiment, the oxygen tank 46 may beeliminated, and air supplied to the cathode side from the ambient.Likewise, the hydrogen tank 48 may be eliminated and hydrogen suppliedto the anode side from a reformer which catalytically generates hydrogenfrom methanol or a liquid hydrocarbon (e.g., gasoline). Exhaust plumbing(not shown) for both the H₂ and O₂/air sides of the MEAs is alsoprovided for removing H₂ depleted anode gas from the anode flow fieldand O₂-depleted cathode gas from the cathode flow field. Coolantplumbing 50 and 52 is provided for supplying and exhausting liquidcoolant to the bipolar plates 14 and 16, as needed.

FIG. 2 depicts an exploded view of the bipolar plate 12, primary currentcollector 38, MEA 10 and primary current collector 40 arranged in astacked relationship in a fuel cell. Bipolar plate 16 would underlie thesecond primary collector 40 (as shown in FIG. 1) to form a fuel cell.Another set of primary current collectors 34 and 36, MEA 8 and bipolarplate 14 would overlie bipolar plate 12 (as shown in FIG. 1) to formanother fuel cell.

The bipolar plate 12 is a single plate member having flow field 20formed therein and made as thin as possible (e.g., about 0.002-0.02inches thick). As presently preferred, the bipolar plates 12, 14 and 16are metal sheets preferably stainless steel that may be formed bystamping, by photoetching (i.e., through a photolithographic mask) orany other conventional process for shaping sheet metal. One skilled inthe art will recognize that other suitable materials and manufacturingprocesses may be utilized from the bipolar plates.

With reference to FIGS. 2-7, the bipolar plate 12 is formed such thatthe geometric configuration of the flow field 20 forms a functionalserpentine flow field 20 s on a first side thereof and a functionalinterdigitated flow field 20 i on the opposite side thereof. Thegeometric configuration of the sementine flow field 20 s iscomolementary to the geometric configuration of the interdigitated flowfield 20 i as illustrated in FIGS. 4 and 6. More specifically, thebipolar plate 12 is formed so as to provide a reactant gas flow fieldcharacterized by a plurality of lands 54 s, 54 i that define a pluralityof flow channels 56 s, 56 i through which the reactant gases flow froman inlet plate margin 58 of the bipolar plate 12 to an exhaust platemargin 60 thereof. The direction of flow across bipolar plate 12 isgenerally from the inlet plate margin 58 through flow field 20 to theoutlet plate margin 60. A plurality of supply header apertures 62 areformed near the outer edge of inlet plate margin 58. A plurality ofinlet ports 64 are formed in the inlet plate margin 58 between thesupply header apertures 62 and the flow field 20. Similarly, a pluralityof exhaust header apertures 66 are formed near the outer edge of outletplate margin 60 and a plurality of exhaust ports 68 are formed in theoutlet plate margin 60 between the exhaust header aperture 66 and flowfield 20. While header apertures 62 and 66 and ports 64 and 68 have beengenerally described, one skilled in the art will readily recognize thateach such aperture and port are dedicated to communicating a specificfluid such as the fuel or the oxidant or the coolant, through the fuelstack. When the fuel cell is fully assembled, the lands 54 s, 54 i pressagainst the primary current collectors 38 and 40 which, in turn, pressagainst the MEA 10. In operation, current generated by the MEA flowsfrom the primary current collectors 38 and 40 through the lands 54 s, 54i and thence through the fuel cell stack. The reactant gases aresupplied to flow channels 56 s, 56 i from supply header aperture 62 viainlet port 64 through the channels 56 and exits exhaust header aperture66 via exhaust port 68.

With reference to FIGS. 2-7, the bipolar plate 12 is formed such thatthe geometric configuration of the flow field 20 forms a functionalserpentine flow field 20 s on a first side thereof and a functionalinterdigitated flow field 20 i on the opposite side thereof. Thegeometric configuration of the sementine flow field 20 s iscomolementary to the geometric configuration of the interdigitated flowfield 20 i as illustrated in FIGS. 4 and 6. More specifically, thebipolar plate 12 is formed so as to provide a reactant gas flow fieldcharacterized by a plurality of lands 54 s, 54 i that define a pluralityof flow channels 56 s, 56 i through which the reactant gases flow froman inlet plate margin 58 of the bipolar plate 12 to an exhaust platemargin 60 thereof. The direction of flow across bipolar plate 12 isgenerally from the inlet plate margin 58 through flow field 20 to theoutlet plate margin 60. A plurality of supply header apertures 62 areformed near the outer edge of inlet plate margin 58. A plurality ofinlet ports 64 are formed in the inlet plate margin 58 between thesupply header apertures 62 and the flow field 20. Similarly, a pluralityof exhaust header apertures 66 are formed near the outer edge of outletplate margin 60 and a plurality of exhaust ports 68 are formed in theoutlet plate margin 60 between the exhaust header aperture 66 and flowfield 20. While header apertures 62 and 66 and ports 64 and 68 have beengenerally described, one skilled in the art will readily recognize thateach such aperture and port are dedicated to communicating a specificfluid such as the fuel or the oxidant or the coolant, through the fuelstack. When the fuel cell is fully assembled, the lands 54 s, 54 i pressagainst the primary current collectors 38 and 40 which, in turn, pressagainst the MEA 10. In operation, current generated by the MEA flowsfrom the primary current collectors 38 and 40 through the lands 54 s, 54i and thence through the fuel cell stack. The reactant gases aresupplied to flow channels 56 s, 56 i from supply header aperture 62 viainlet port 64 through the channels 56 and exits exhaust header aperture66 via exhaust port 68.

With reference now to FIGS. 3, 4 and 7, the serpentine flow field 20 swill be described in further detail. Serpentine flow field 20 s includesan inlet feed 70 providing fluid communication into flow channel 56 swhich traverses the width of the bipolar plate 12 and terminates atexhaust feed 72. Flow channel 56 s is defined by a first serpentine path74 having plurality of medial legs 76 extending transversely on thebipolar plate 12 and a second serpentine path 78 having a plurality ofmedial legs 80 extending transversely on the bipolar plate 12. First andsecond serpentine paths 74, 80 each traverse approximately one-half thewidth of the bipolar plate 12 and are fluidly coupled by a crossover leg82. As best seen in FIG. 4, the adjacent interior serpentine flowchannels 56 s are supplied by a common inlet feed 70 and share a commonexhaust feed 72. Hence, the inlet legs of the adjacent flow channels arecontiguous to each other at the inlet feed 70, and the outlet legs ofthe adjacent flow channels are contiguous to each other at the exhaustfeed 72. Effectively, each flow channel is a mirror image of the nextadjacent flow channel. Reactant gases flowing in serpentine flowchannels 56 s may also flow through the primary current collector 36 toan adjacent flow channel 56 s as illustrated in FIG. 7.

With reference now to FIGS. 5-7, the interdigitated flow field 20 i willnow be described. Flow channels 56 s formed on the serpentine side 20 sof the bipolar plate 12 define lands 54i on the opposite side, andlikewise lands 54 s on the serpentine side 20 s of bipolar plate 12define flow channels 56 i on the opposite side thereof that arecomplementary to each other. As best seen in FIG. 6, interdigitated flowfield 20 i includes an inlet feed 84 providing fluid communication intoflow channel flow 56 i which traverses the width of bipolar plate 12 andterminates at exhaust feed 86. As with the serpentine flow channels 56s, the interdigitated flow channels 56 i are divided into a firstinterdigitated flow path 88 having a plurality of medial legs 90 influid communication with the inlet feed 84 and a plurality of mediallegs 92 in fluid communication with exhaust feed 86 which traverse thefirst half of the bipolar plate and a second interdigitated flow path 94having a plurality of medial legs 96 in fluid communication with theinlet feed 84 and a plurality of medial legs 98 in fluid communicationwith exhaust feed 86 which traverse the second half of the bipolar plate12. Reactant gas flowing in the interdigitated flow paths 88, 94 frominlet feed 84 must cross over land 54 i through the primary currentcollector 40 to be discharged through exhaust feed 86, as best seen inFIG. 7.

Referring now to FIG. 8, a partial isometric exploded view of a PEM fuelstack 100 having an uncooled fuel cell 102 u and a cooled fuel cell 102c is illustrated. Uncooled fuel cell 102 u includes MEA/primary currentcollector assembly 106, seal 108, bipolar plate 110, and seal 112arranged in a stacked relationship. The cooled fuel cell 102 c includesMEA/current conductor assembly 114, seal 116, bipolar plate 118, spacer120, bipolar plate 122 and seal 124. One skilled in the art will readilyrecognize that while PEM fuel stack 100 is shown having one uncooledfuel cell 102 u and one cooled fuel cell 102 c, the ratio of cells withcooling to cells without cooling in the stack is variable depending onthe operating characteristic of the stack. As such any ratio (e.g., 1,{fraction (1/2, α, 1/4)}, . . . ) is contemplated by the presentinvention. In addition, an air cooled stack (i.e. having a ratio of Ø)which uses the reactant air for cooling is also contemplated by thepresent invention.

Bipolar plates 110, 118 and 122 have a flow field 126 definingserpentine flow channels formed on the upper surface thereof andinterdigitated flow channels formed on the lower surface thereof asheretofore described. A series of rectangular supply header apertures128 (oxidant), 130 (fuel) and 132 (coolant) are formed through thebipolar plates 110, 118 and 120 for communicating the gaseous reactants(i.e., the oxidant and the fuel) and coolant, respectively from theplumbing 42 (oxidant), 44 (fuel) and 50 (coolant) through the fuelstack. In this regard, the bipolar plates 110, 118 and 122 are arrangedin a stacked relationship such that the apertures 128, 130 and 132 alignto form fluid feed tunnels axially through the fuel stack. Bipolarplates 110, 118 and 122 also have ports 134, 136 and 138 formed thereinfor directing gaseous reactants and coolant respectively from the supplyheader apertures 128, 130 and 132 to the appropriate flow field 126.

The present invention utilizes a staggered seal arrangement which formfluid communication paths from the header apertures through the ports tothe flow fields. Specifically, the configuration of seals 108, 112, 116and 124 as well as spacer 120 define such fluid communication pathsdepending upon the fluid flowing therethrough.

With reference now to FIGS. 8 through 14, the staggered sealconfiguration of the present invention will be described in furtherdetail. In the case of the fuel flow through the cooled cell 102 c, areactant fuel gas, is communicated from supply header aperture 130 belowbipolar plate 118 through anode port 136 above bipolar plate 118 to theanode side of MEA 114 through a stepped seal configuration. Morespecifically, spacer 120 has an aperture 140 formed therein whichincludes a fluid communication path 142 circumscribing anode port 136formed in bipolar plate 118. Seal 116 located on the opposite side ofbipolar plate 118 from spacer 120 includes a fluid communication path144 which also circumscribes anode port 136 formed in bipolar plate 118and terminates at inlet leg 146. A similar fluid communication path isestablished for uncooled fuel cell 102 u in that aperture 148 formed inseal 112 has a fluid communication path 150 extending therefrom suchthat the seal 112 circumscribes anode port 136 formed in bipolar plate110. Seal 108 located on the opposite side of bipolar plate 110 has afluid communication path 152 extending from an inner periphery thereofto circumscribe anode port 136 formed in bipolar plate 110 andterminates at inlet leg 154.

With particular reference now to FIG. 10, the anode fluid flow path toMEA 114 is illustrated. Fuel flows through supply header aperture 130along fluid communication path 142 defined by bipolar plate 118, spacer120 and bipolar plate 122 through anode port 136 and along fluidcommunication path 144 defined by MEA 114, seal 116 and bipolar plate118. Similarly, with reference to FIG. 11, the anode fluid flow path toMEA 106 is illustrated. Fuel flows through supply header aperture 136along fluid communication path 150 defined by bipolar plate 110, seals112, 116 and bipolar plate 118 through anode port 136 formed in bipolarplate 110 and then along fluid communication path 152 defined by MEA106, seal 108 and bipolar plate 110. In each of these instances, theanode fluid flow path directs fuel from the fuel supply to the anodeface of MEA 106 and 114.

In the case of oxidant flow through the uncooled cell 102 u, a reactantoxidant gas is communicated from supply header aperture 128 abovebipolar plate 110 through cathode port 134 below bipolar plate 110 tothe cathode side of MEA 114 through a stepped sealed configuration. Morespecifically, seals 105, 108 have an aperture 156 formed therein whichincludes a fluid communication path 158 circumscribing cathode port 134formed in bipolar plate 110. Seal 112 located on the opposite side ofbipolar plate 110 from seal 108 includes a fluid communication path 160which also circumscribes cathode port 134 formed in bipolar plate 110and terminates at inlet leg 154. A similar fluid communication path isestablished for cooled fuel cell 102 c is defined by the staggered sealconfiguration.

With particular reference now to FIG. 12, the cathode fluid flow path toMEA 114 is illustrated. Oxidant flows through supply header aperture 128along fluid communication path 158 defined by bipolar plate 104, seals105, 108 and bipolar plate 110 through cathode port 134 and then alongfluid communication path 160 defined by bipolar plate 110, seal 112 andMEA 114. Similarly, with reference to FIG. 13, oxidant flows throughsupply header aperture 128 above bipolar plate 104 through cathode port134 and then along fluid communication path 162 defined by bipolar plate104, seal 105 and MEA 106.

With reference now to FIG. 14, the cooled fuel cell 102 c flow path isillustrated. A coolant is communicated from supply header aperture 132between bipolar plates 110 and 118, through coolant port 138 belowbipolar plate 118 through a stepped sealed configuration. Morespecifically, seals 112, 116 have an aperture 164 formed therein whichincludes a fluid communication path 166 circumscribing coolant port 138formed in bipolar plate 118. Spacer 120 located on the opposite side ofbipolar plate 118 includes a fluid communication path 168 which alsocircumscribes coolant port 138 formed in bipolar plate 118 andterminates at an interior coolant volume 170.

Coolant flows through supply header aperture 132 along fluidcommunication path 166 defined by bipolar plate 110, seals 112, 116 andbipolar plate 118 through coolant port 138 and then along fluidcommunication path 168 defined by bipolar plate 118, spacer 120 andbipolar plate 122 into an interior coolant volume 170 defined betweenthe flow fields formed on bipolar plate 118 and bipolar plate 122.

The supply or inlet flow of fluid into the fuel stack 100 has beendescribed above in particular detail. One skilled in the art willreadily recognize that the staggered seal configuration of the presentinvention incorporates a similar staggered seal configuration on theexhaust side of the fuel stack 100 for exhausting the gaseous reactantsand coolant from the fuel stack. Thus, through the use of the steppedsealed arrangement described above, the present invention is able toefficiently transport the gaseous reactants and coolant into, throughand out of the fuel stack 100.

While the present invention has been described through the use of a sealdisposed on either side of the MEAs (i.e. a pair of seals), one skilledin the art would readily recognize that a single seal could besubstituted in this arrangement without deviating from the spirit andscope of the present invention. Furthermore, while the present inventionhas been described as using the serpentine flow field for the anode sideof the fuel cell and the interdigitated flow field for the cathode sideof the fuel cell, one skilled in the art would readily recognize thatthe interdigitated flow field may have certain utility for use on theanode side of the fuel cell, and likewise the serpentine flow field mayhave certain utility for use on the cathode side of the fuel cell asdetermined by the particular application. Thus, while the invention hasbeen disclosed in terms of various preferred embodiments, it is notintended that the present invention be limited thereto but rather onlyto the extent set forth hereafter in the claims which follow.

1. A flow field plate for use in a fuel cell comprising a thin platehaving an inlet margin including a first inlet header and a second inletheader formed therethrough, an exhaust margin including a first exhaustheader and a second exhaust header formed therethrough, and a flow fieldformed therein, said flow field having a plurality of first channelsformed in a first major face of said thin plate and configured toprovide an interdigitated flow field between said first inlet header andsaid first exhaust header, said plurality of first channels forming aplurality of lands in a second major face of said thin plate oppositesaid first major face which define a plurality of second channelsconfigured to provide a serpentine flow field between said second inletheader and said second exhaust header.
 2. The flow field plate of claim1 wherein said interdigitated flow field comprises an inlet leg in fluidcommunication with said first inlet header, an exhaust leg in fluidcommunication with said first exhaust header and an interdigitated flowchannel having a first end in fluid communication with said inlet legand a second end in fluid communication with said exhaust leg.
 3. Theflow field plate of claim 2 wherein said interdigitated flow fieldfurther comprises a first interdigitated flow channel located adjacentsaid inlet margin and a second interdigitated flow channel locatedadjacent said exhaust margin, each of said first and secondinterdigitated flow channels having a first plurality of medial legs influid communication with said inlet leg and a second plurality of mediallegs in fluid communication with said exhaust leg.
 4. The flow fieldplate of claim 3 wherein said inlet leg comprises a first lateralportion in fluid communication with said first interdigitated flowchannel, a second lateral portion in fluid communication with saidsecond interdigitated flow channel, and a transverse portion extendingthrough said first interdigitated flow channel between said first andsecond lateral portions.
 5. The flow field plate of claim 4 wherein saidtransverse portion extends substantially the length of said firstplurality of medial legs.
 6. The flow field plate of claim 4 whereinsaid exhaust leg comprises a third lateral portion in fluidcommunication with said first interdigitated flow channel, a fourthlateral portion in fluid communication with said second interdigitatedflow channel, and a pair of transverse portions extending between saidthird and fourth lateral portions and bordering said secondinterdigitated flow channel.
 7. The flow field plate of claim 6 whereinsaid pair of transverse portions extend substantially the length of saidsecond plurality of medial legs.
 8. The flow field plate of claim 3wherein said exhaust leg comprises a first lateral portion in fluidcommunication with said first interdigitated flow channel, a secondlateral portion in fluid communication with said second interdigitatedflow channel, and a pair of transverse portions extending between saidfirst and second lateral portions and bordering said secondinterdigitated flow channel.
 9. The flow field plate of claim 8 whereinsaid pair of transverse portions extend substantially the length of saidsecond plurality of medial legs.
 10. The flow field plate of claim 1wherein said serpentine flow field comprises an inlet leg in fluidcommunication with said second inlet header, an exhaust leg in fluidcommunication with said second exhaust header and a serpentine flowchannel having a first end in fluid communication with said inlet legand a second end in fluid communication with said exhaust leg.
 11. Theflow field plate of claim 10 wherein said serpentine flow field furthercomprises a first serpentine flow channel and a second serpentine flowchannel adjacent said first serpentine flow channel, each of said firstand second serpentine flow channels having a first end in fluidcommunication with said inlet leg and a second end in fluidcommunication with said exhaust leg.
 12. The flow field plate of claim11 wherein said second serpentine flow channel is a mirror image of saidfirst serpentine flow channel.
 13. The flow field plate of claim 10wherein said serpentine flow field further comprises: a first serpentinepath formed adjacent said inlet margin and having a first end in fluidcommunication with said inlet leg and a second end; a second serpentinepath formed adjacent said exhaust margin and having a first end and asecond end in fluid communication with said exhaust leg; and a crossoverleg interposed between said first and second serpentine paths, saidcrossover leg in fluid communication with said second end of said firstserpentine path and said first end of said second serpentine path. 14.The flow field plate of claim 1 wherein said thin plate furthercomprises: said inlet margin having a first inlet port formedtherethrough to provide fluid communication from said first inlet headerto said interdigitated flow field, and a second inlet port formedtherethrough to provide fluid communication from said second inletheader to said serpentine flow field; and said exhaust margin having afirst exhaust port formed therethrough to provide fluid communicationfrom said interdigitated flow field to said first exhaust header, and asecond exhaust port formed therethrough to provide fluid communicationfrom said serpentine flow field to said second exhaust header.
 15. Aflow field geometry in a separator plate of a fuel cell, said flow fieldgeometry comprising: an inlet feed in fluid communication with an inletheader; an exhaust feed in fluid communication with an exhaust header;and an interdigitated flow field having a first interdigitated flowchannel formed adjacent said inlet feed and a second interdigitated flowchannel formed adjacent said exhaust feed each of said first and secondinterdigitated flow channels having a first plurality of medial legs influid communication with said inlet feed and a second plurality ofmedial legs in fluid communication with said exhaust feed.
 16. The flowfield geometry of claim 15 wherein said inlet feed comprises a firstlateral portion in fluid communication with said first interdigitatedflow channel, a second lateral portion in fluid communication with saidsecond interdigitated flow channel, and a transverse portion extendingthrough said first interdigitated flow channel between said first andsecond lateral portions.
 17. The flow field geometry of claim 16 whereinsaid transverse portion extends substantially the length of said firstplurality of medial legs.
 18. The flow field geometry of claim 16wherein said exhaust feed comprises a third lateral portion in fluidcommunication with said first interdigitated flow channel, a fourthlateral portion in fluid communication with said second interdigitatedflow channel, and a pair of transverse portions extending between saidthird and second lateral portions and bordering said secondinterdigitated flow channel.
 19. The flow field geometry of claim 18wherein said pair of transverse portions extend substantially the lengthof said second plurality of medial legs.
 20. The flow field geometry ofclaim 15 wherein said exhaust feed comprises a first lateral portion influid communication with said first interdigitated flow channel, asecond lateral portion in fluid communication with said secondinterdigitated flow channel, and a pair of transverse portions extendingbetween said first and second lateral portions and bordering said secondinterdigitated flow channel.
 21. The flow field geometry of claim 20wherein said pair of transverse portions extend substantially the lengthof said second plurality of medial legs.
 22. In a fuel cell of the timehaving a separator plate interposed between a pair of electrodes, saidseparator plate comprising: a single plate having a first major face anda second major face opposite said first major face; a first flow fieldhaving a first geometric configuration formed in said first major facefor transporting a first reactant gas to a major face of a firstelectrode; a second flow field having a second geometric configurationformed in said second major face which is complementary to said firstgeometric configuration for transporting a second reactant gas to amajor face of a second electrode; wherein said first geometricconfiguration forms an interdigitated flow field and said secondgeometric configuration forms a serpentine flow field; and wherein saidinterdigitated flow field comprises a first interdigitated flow channeladjacent an inlet leg and a second interdigitated flow channel locatedadjacent an exhaust leg, each of said first and second interdigitatedflow channels having a first plurality of medial legs in fluidcommunication with said inlet leg and a second plurality of medial legsin fluid communication with said exhaust leg.
 23. The separator plate ofclaim 22 wherein said inlet leg comprises a first lateral portion influid communication with said first interdigitated flow channel, asecond lateral portion in fluid communication with said secondinterdigitated flow channel, and a transverse portion extending throughsaid first interdigitated flow channel between said first and secondlateral portions.
 24. The separator plate of claim 23 wherein saidtransverse portion extends substantially the length of said firstplurality of medial legs.
 25. The separator plate of claim 23 whereinsaid exhaust leg comprises a third lateral portion in fluidcommunication with said first interdigitated flow channel, a fourthlateral portion in fluid communication with said second interdigitatedflow channel, and a pair of transverse portions extending between saidfirst and second lateral portions and bordering said secondinterdigitated flow channel.
 26. The separator plate of claim 25 whereinsaid pair of transverse portions extend substantially the length of saidsecond plurality of medial legs.
 27. The separator plate of claim 22wherein said exhaust leg comprises a first lateral portion in fluidcommunication with said first interdigitated flow channel, a secondlateral portion in fluid communication with said second interdigitatedflow channel, and a pair of transverse portions extending between saidfirst and second lateral portions and bordering said secondinterdigitated flow channel.
 28. The separator plate of claim 27 whereinsaid pair of transverse portions extend substantially the length of saidsecond plurality of medial legs.
 29. In a fuel cell of the type having aseparator plate interposed between a pair of electrodes, said separatorplate comprising: a single plate having a first major face and a secondmajor face opposite said first major face; a first flow field having afirst geometric configuration formed in said first major face fortransporting a first reactant gas to a major face of a first electrode;a second flow field having a second geometric configuration formed insaid second major face which is complementary to said first geometricconfiguration for transporting a second reactant gas to a major face ofa second electrode; wherein said first geometric configuration forms aninterdigitated flow field and said second geometric configuration formsa serpentine flow field; and wherein said serpentine flow fieldcomprises a first serpentine path having a first end in fluidcommunication with an inlet leg and a second end, a second serpentinepath having a first end and a second end in fluid communication with anexhaust leg, and a crossover leg in fluid communication with said secondend of said first serpentine path and said first end of said secondserpentine path.
 30. The separator plate of claim 22 wherein said singleplate further comprises: an inlet margin having a first inlet portformed therethrough to provide fluid communication from a first inletheader to said first flow field, and a second inlet port formedtherethrough to provide fluid communication from a second inlet headerto said second flow field; and an exhaust margin having a first exhaustport formed therethrough to provide fluid communication from said firstflow field to a first exhaust header, and a second exhaust port formedtherethrough to provide fluid communication from said second flow fieldto a second exhaust header.